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<br>
(again, hoping to help someone or another) <br>
<br>
Two prong receptacles in old wiring connect one prong <br>
to the "hot" lug at the service and depend on the bonding <br>
between the neutral lug and the ground lug at the service <br>
entrance so that the neutral wire is also the path to earth <br>
ground. <br>
The receptacle has a cover that is attached to the <br>
receptacle itself by a small (#6-32) screw. This screw is <br>
electrically connected to the neutral and can serve as a <br>
"separate" ground lug. <br>
To power a device with a three prong plugs to a two <br>
prong receptacle, get an adapter (about a dollar at any <br>
hardware store). Note the plug for your device fits in at <br>
one end of the adapter and the other end of the adapter <br>
has two prongs and a small (usually green) tab. <br>
Some adapters' prongs are "modern" such that the <br>
neutral prong is wider than the hot prong. Some two-<br>
prong receptacles accommodate such adapters, and <br>
some do not--they present connections for two, <br>
similarly sized prongs, both small. It's probably good <br>
to buy an adapter with two small prongs (not only will <br>
it fit all receptacles, you can turn it "upside down" to <br>
try to reduce noise or shock hazard. <br>
The (green) tab attaches to the plate cover screw. <br>
Before you plug the adapter in, remove the screw, <br>
then plug in the adapter, then screw back the plate <br>
cover screw through the (green) tab. This not only <br>
gives your device a pseudo-separate ground path, it <br>
fastens the adaptor to the socket, providing pretty <br>
good strain relief. <br>
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<br>
<div class="moz-cite-prefix">On 02/08/2015 12:14 PM, Hermann Meyer
wrote:<br>
</div>
<blockquote
cite="mid:f35a8fbe-fb90-42f9-89bb-f8e7fc928399@email.android.com"
type="cite">Old buildings didn't use grounds, they just have 2
cords and use the second as ground and backline. In German this is
called Nullung.<br>
Potential issues are clear with this technique.<br>
-- <br>
<br>
<br>
<div class="gmail_quote"><br>
<br>
Ralf Mardorf <a class="moz-txt-link-rfc2396E" href="mailto:ralf.mardorf@alice-dsl.net"><ralf.mardorf@alice-dsl.net></a> schrieb:
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">
<pre style="white-space: pre-wrap; word-wrap:break-word; font-family: sans-serif">On Sun, 8 Feb 2015 09:06:40 -0800 (PST), Len Ovens wrote:
>It appears we have power coming from two power entrances with two
>different earth grounds to the panels.
I experienced potential difference for the ground in old buildings
between two main sockets, less than 3 meters difference between those
sockets, both fed by the same power, coming from the same fuse and
connected to the same concrete-footing ground electrode.
Even if the power should come from two different sources, one building
should have one concrete-footing ground electrode for ground, so in
theory there shouldn't be a potential difference.
Buildings sometimes don't care about school books.
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